Split the stdsimd feature into separate features #1845

Job	Run time
Check Style	19s
Automatic intrinsic verification	43s
Env Override	19s
Build std_detect	1m 28s
Build Documentation	1m 38s
Test (i686-unknown-linux-gnu)	3m 1s
Test (x86_64-unknown-linux-gnu)	4m 44s
Test (x86_64-unknown-linux-gnu-emulated)	4m 47s
Test (arm-unknown-linux-gnueabihf)	2m 20s
Test (armv7-unknown-linux-gnueabihf)	4m 43s
Test (aarch64-unknown-linux-gnu)	4m 43s
Test (riscv64gc-unknown-linux-gnu)	2m 36s
Test (powerpc64le-unknown-linux-gnu)	4m 25s
Test (s390x-unknown-linux-gnu)	3m 4s
Test (wasm32-wasi)	3m 10s
Test (i586-unknown-linux-gnu)	4m 6s
Test (nvptx64-nvidia-cuda)	44s
Test (thumbv6m-none-eabi)	19s
Test (thumbv7m-none-eabi)	21s
Test (thumbv7em-none-eabi)	20s
Test (thumbv7em-none-eabihf)	19s
Test (aarch64-apple-darwin)	2m 21s
Test (x86_64-pc-windows-msvc)	4m 36s
Test (i686-pc-windows-msvc)	4m 39s
Test (x86_64-apple-darwin, macos-11)	4m 41s
	1h 4m 26s

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